The present invention relates to internal combustion engines, and more particularly to improved means for supporting a thermocouple junction in the stream of a gas flowing through an engine.
Since its inception, both the maintenance and development of the internal combustion engine have required analytical apparatus. Over the years, varied and sophisticated means have been developed for monitoring the operation of these engines. Trucks, automobiles and airplanes are commonly furnished with instrumentation for monitoring engine vacuum, temperature, and oil pressure and repair shops are often provided with facilities for testing engine compression, electrical characteristics, and exhaust gas composition.
One aspect of internal combustion engine operation which has to date been little used for monitoring automotive engine operation is the exhaust gas temperature. Although it is known to monitor temperature of the exhaust gases of aircraft by means of thermometers, thermocouples or related devices, for automobiles this approach has been substantially restricted to laboratory or controlled field tests.
The principal drawback to the monitoring of exhaust temperature is an economic one and involves the mounting of the thermal sensing unit. Aircraft engines tend to be relatively expensive mechanisms, and the incremental cost of the thermal sensors is not generally considered to be significant. Further, the construction of aircraft engines lends itself well to the implementation of thermal sensing mountings in that exhaust manifolds are commonly fabricated from tubular material and thus have relatively uniform dimensional characteristics. It is a relatively simple task to drill a hole in such a manifold, insert a probe through the hole, and attach the probe to the manifold by means of a clamping strap arrangement. Most automobiles and trucks, however, utilize cast iron manifolds. In view of the irregular configurations of such manifolds, simple clamping arrangements have been found unsatisfactory. In order to mount the thermal sensors in the exhaust streams of automobiles, an almost universal procedure is to drill and tap the manifolds to receive a threaded mounting gland. Such drilling and tapping operations are relatively expensive and are not easily accomplished in the garages and small repair shops which perform most of the maintenance and repair work upon privately-owned vehicles.
A still further problem in inserting probes through cast manifold walls is that, due to the irregular configuration of the manifolds, it is often impossible to place the probes at identical distances from each cylinder port. Due to the rapid change in the temperature of the exhaust streams, it is necessary that the thermal probes be placed in identical positions in order to obtain meaningful readings.
In one popular but strictly analytical approach thermocouple mountings are formed in combination with the spark plugs of an engine. While such devices may lend themselves to analytical work under controlled conditions the scope of their use is relatively limited. The devices are expensive, and moreover are typically exposed to the high voltages which are applied to the spark plug. Further, they serve to sense the temperature at only a single point in the combustion chamber. It is generally known that temperatures vary greatly within the combustion chambers of internal combustion engines, so that the temperature encountered at one point therein may not be representative of the overall combustion process.
With the advent of the stratified charge engine and the increasing need for pollution-free power plants, the need for monitoring engine combustion has increased. Further, it has been found that state-of-the-art exhaust gas analyzers are not adaptable for use with stratified charge engines. Accordingly, an increased need has arisen for superior engine monitoring means which can be installed in motor vehicles quickly and inexpensively.
It is therefore an object of the present invention to provide an improved thermal sensing means for an internal combustion engine.
Another object of the invention is to provide simplified means for mounting a thermocouple in a stream of gas flowing through an engine.
It is another object of the invention to provide a thermocouple mounting structure which produces a more uniform reading than those heretofore known.
Yet another object of the invention is to provide an associated thermocouple and mounting means which may be installed in a motor vehicle easily, without modification thereto.